Nowadays, ORC is the most efficient solution to convert low-to-medium heat to electricity. The priciple of ORC is quite the same with Rankine cycle, but use the low boiling temperature refregerant as working fluid instead of water in Rankine cycle. The main components are: working fluid pump, evaporator, expander-generator, condenser. For different temperature heat application, suitable working fluid is selected. Following describes the working principle. 

1→2：Liquid working fluid is pumped to high pressure, and be sent to evaporator.

2→3：In evaporator, liquid working fluid absorbs the heat from heat source and vaporized to vapor, then moves to expander.

3→4：High temperature, high pressure vapor working fluid expands in expander, making the expander rotating and then generating power. After expansion, the working fluid becomes low temperature, low pressure vapor, and then flows to condenser. 

4→1：Vapor working fluid condenses to liquid phase by heat sink in condenser, then goes back to pump, completes the cycle.

The thermal efficiency of ORC is mainly effected by the difference between designed evaporation temperature and condensing temperature. The higher temperature difference will result in a higher thermal efficiency. Furthermore, different working fluid also performs differenct thermal efficiency.